The present invention relates to an optical disk apparatus for optically recording information on an optical disk through the use of laser light and to an optical disk recording method used in the optical disk recording apparatus.
In the optical disk apparatus for recording data in the optical disk using laser light and reproducing binarized information from the optical disk, when recording the data, recording parameter learning is required for optimally adjusting the power and timing of a recording laser pulse (hereinafter referred to as “record strategy”)
In the recording parameter learning, the quality of the record is evaluated based on the quality of reproduced recorded data. In this event, if data recording velocity differs from data reproducing velocity, every time switching is performed between the recording and reproduction, the rotational velocity has to be changed, posing problems including the generation of heat incident to the variation of torque of a spindle motor for rotating the optical disk as well as the occurrence of a waiting time before a spindle motor rotates with a desired number of rotations. In order to prevent this, it is preferable to equalize the velocity at which to record the data of the recording parameter learning to that at which to reproduce the data of the recording parameter learning.
The frequency characteristic of a reproduction system that is formed of a photoelectric conversion circuit for converting reproduction light from the optical disk into an electrical signal, an electric signal transmission circuit, a processing circuit or the like is limited. Therefore, as the reproduction velocity of the optical disk becomes higher and the frequency of the binarized information becomes higher, signal amplitude and signal SN ratio decrease, or interference occurs between signal codes, thus causing errors in the determination of binarized signals during reproduction.
In other words, there is a problem that when trying to reproduce data at the same velocity as recording velocity in high speed recording and to evaluate the quality thereof, the waveform sometimes exhibits distortion due to the lack of a signal transmission band. One of the indexes for evaluating the record quality is a jitter that indicates the fluctuation of an edge position of a reproduced signal, which is information reproduced after being recorded in the optical disk. When the waveform exhibits the distortion, however, it becomes difficult to correctly detect jitters from the reproduced signal.
As a method of reducing error in determining binarized signal during the reproduction, PRML (Partial Response and Maximum Likelihood) processing is well known. The PRML is a method of adaptively equalizing the signal reproduced from the optical disk such that it reaches a known PR (Partial Response) class in which interference between codes is permitted, and estimating a signal sequence that looks most definite by means of ML (Maximum Likelihood) that follows the equalization target of the PR class and determining the binarization. Moreover, according to the PRML, a binarized signal can be reproduced in a stable manner even when the band of the reproduction system is low relative to the band of the reproduced signal. As a method of determining the record quality when the PRML processing is used, methods are proposed that determine the record quality from a difference value from the PR equalization target (refer to Japanese Laid-open Patent Applications 2003-006864, and 2005-339690)